DannyBoy81

I herd of Lack salt in the diet can cause it too.....! and Lack of fluids while training.

Just found this (COPY AND PASTE JOBBY)

Causes
Overuse of a muscle, dehydration, injury, muscle strain or simply holding a position for prolonged periods of time may result in a muscle cramp. Athletes who become fatigued and dehydrated while participating in warm-weather sports frequently develop muscle cramps. Muscle cramps in your legs also can result from:

Inadequate blood supply. Narrowing of the arteries that deliver blood to your legs (arteriosclerosis of the extremities) can produce cramp-like pain in your legs and feet while you're exercising. These cramps go away within a minute or two after you stop exercising and stand still.
Nerve compression. Compression of nerves in your spine (lumbar stenosis) also can produce cramp-like pain in your legs. The pain usually worsens the longer you walk. Walking in a slightly flexed position — such as you would when pushing a shopping cart ahead of you — may improve your symptoms.
Mineral depletion. Too little potassium, calcium or magnesium in your diet can contribute to leg cramps. Some diuretic medications prescribed for high blood pressure cause loss of potassium.
Muscle cramps are also part of certain conditions such as nerve, thyroid or hormone disorders, diabetes, hypoglycemia and anemia.